The traditional three piece railway freight car truck consists of one bolster and two side frames. The side frames are supported at their ends by the wheelsets. The bolster which carries the car body extends centrally through the side frames. The bolster is supported on suspension springs with damping friction shoes located in the side frames that support the bolster. The suspension contains load springs that support the bolster and control springs that support the friction shoes. The friction shoes include angled surfaces that bear against the bolster in pockets that have mating angled surfaces. The result of the spring three acting on friction shoe against the angled support of the bolster is a wedge force acting on the side frame. Damping is the result of the wedge force on the friction shoe flat surface sliding against and along the flat surface of the side frame. The resulting wedge force and friction between the friction shoe flat surface and the side frame flat surface creates sliding force resistance to movement. The friction shoe sliding force resistance increases as the springs are compressed. The friction shoe sliding force resistance is primarily intended for vertical damping; however the friction shoe sliding force resistance is also coupled to lateral movement.
The traditional three piece railway freight truck speed is limited due to lateral track displacement irregularities that initiate uneven steering force at the wheels. The uneven steering force accompanied by the truck and car body inertias cause the trucks to steer or yaw. The instability process repeats itself describing a sinusoidal path that increases with speed of the freight car. The instability is called hunting and is inherent to the tapered wheel tread surface design as used in a traditional three piece railway freight truck. Lateral track displacement irregularities transmitted to the wheelsets and into the side frames create lateral displacement of the side frames. The lateral displacement of the side frames is transmitted through the friction shoes and into the bolster and finally from the bolster into the car body. The lateral displacement provides the energy necessary to displace the car body. The displacement energy then rebounds with sufficient inertia to return the car body back through the neutral position. The displacement energy inertia continues back through the truck, and through the wheelsets. Each pair of tapered wheels is rigidly connected by an axle. The rigidly connected wheels and axle are referred to as a wheelset. Lateral displacement between the wheelset to the track position creates difference in the rolling radius of the tapered wheels. The rolling radius change creates a difference in the distance each wheel travels along the rails, which yaw the wheelset and attempts to turn the truck. This leads to instability of the truck on the rails and excess wheel wear.
The present invention relates to decoupling the displacement energy path from the wheelset to the car body and the car body rebound energy back to the wheelsets. Laterally decoupling the ability of friction shoes to transmit displacement energy to or from the wheelsets or the car body prevents displacement energy from displacing the wheelsets in relation to the track. This in turn prevents wheelset yaw and the sinusoidal path of the freight car truck as it travels along the rails.